Perhaps brevity is elusive for a man who once held the Theodore and Frances Geballe Professor of Physics and Applied Physics chair at Stanford University and is credited with producing one of the earliest atomic physics confirmations of the Weinberg-Salam-Glashow theory that unifies the weak and electromagnetic forces.

Energy Secretary Steven Chu announced his resignation today in a 3,800-word, bullet-pointed “Dear Colleague” letter. Posted on the agency’s Web-site, it runs six pages when printed.

“I came with dreams, and am leaving with a set of accomplishments that we should all be proud of,” Chu, who won the 1996 Nobel Prize for Physics, wrote in his letter, which quotes Martin Luther King, Michelangelo and an ancient Native American proverb that “we do not inherit the land from our ancestors, we borrow it from our children.”

The memo reads as much as a clean-energy manifesto and rebuke to critics as a goodbye to the agency. It lists more than 30 accomlishments — from a doubling of wind and solar energy and energy conservation upgrades to 1 million low-income homes to his personal involvement in capping BP Plc’s oil spill and the department’s “crucial role” in launching a clean-energy “ministerial.”

“In the scientific world, people are judged by the content of their ideas,” Chu wrote.

In places, the letter reads like a response to one of Chu’s and the department’s biggest stumbles: the half-billion dollar loan to Solyndra, a solar panel maker that went bankrupt two years later.

While the letter doesn’t mention the ‘S’ word, Chu does make a few veiled references to criticism from Republicans that Solyndra shows the folly of trying to pick “winners and losers” among companies.

“While critics try hard to discredit the program, the truth is that only 1 percent of the companies we funded went bankrupt,” Chu wrote of the Energy Department’s loan program.

Quoting Michelangelo, Chu wrote: “The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low, and achieving our mark.”

“The test for America’s policy makers will be whether they are willing to accept a few failures in exchange for many successes,” Chu said.

The U.S. should continue to aim high, he encouraged. The letter ends with a passionate appeal to address the challenges of a warming planet.

“Ultimately we have a moral responsibility to the most innocent victims of adverse climate change,” Chu wrote. “Those who suffer the most are the people who are the most innocent: the world’s poorest citizens and those yet to be born.”

Policymakers, Chu said, should be judged “by the content of our decisions.”